Fluidized bed combustion system with steam generation

ABSTRACT

A solid fuel fluidized-bed steam generator in which a pair of combustion chambers straddle a heat-exchange chamber of rectangular configuration in a row and have one or more gas/solids separators connected to the combustion chambers at the tops thereof and lines which deliver gas from the separators to the heat-exchange chamber. The heat-exchange chamber has a plurality of heat-exchange elements for indirect heat exchange between hot gas and a cooling fluid, for example water, which is converted to steam.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a national stage of PCT/EP99/03376 filed May 17, 1998 and basedupon German national applications 198 22 304.8 of May 18, 1998 and 19834 881.9 of Aug. 1, 1998 under the International Convention

FIELD OF THE INVENTION

This invention relates to a fluidized-bed firing system with generationof steam for the combustion of solid fuels and for generating steam.

BACKGROUND OF THE INVENTION

Such systems, which are advantageous for smaller power outputs, areknown for instance from EP-B-0365723, EP-A-0416238 as well asDE-A-3107356 and DE-A-4135582. In the known plants, only a singlefluidized-bed combustion chamber is associated with a heat-exchangechamber. For large plants, which generate a large amount of steam thatis used in power plants with more than 250 MW (electrical) capacity, theknown systems are not advantageous.

OBJECT OF THE INVENTION

It is the object of the invention to provide a fluidized-bed firingsystem in a compact design such that it can be built as a blockrequiring little space.

SUMMARY OF THE INVENTION

In accordance with the invention this achieved in

a) that in a heat-exchange chamber with an inner (internal) height of atleast 10 m, there are disposed heat-exchange elements through whichflows a cooling fluid, and the heat-exchange chamber has four verticalouter walls which enclose a space approximately rectangular inhorizontal cross-section.

b) that outward of a first outer wall of the heat-exchange chamber afirst fluidized-bed combustion chamber is disposed, and outwardly of asecond outer wall of the heat-exchange chamber opposite the first outerwall a second fluidized-bed combustion chamber is disposed, where theinner height of the fluidized-bed combustion chamber is 10 to 60 m andpreferably at least 20 m, and each fluidized-bed combustion chamber haslines for supplying fuel and combustion air, and

c) that with the upper portion of each fluidized-bed combustion chamberat least one separator is connected for separating solids from a gasstream, which separator has at least one gas-carrying discharge lineconnected with the heat-exchange chamber.

In one embodiment of the invention, each fluidized-bed combustionchamber is associated with at least one fluidized-bed cooler which isdisposed below a separator and is connected therewith by asolids-carrying line. Each fluidized-bed cooler is connected with theassociated fluidized-bed combustion chamber through at least one linecarrying solids and/or gas.

The plant in accordance with the invention can be designed and build asa compact block. At the same time it is possible easily to arrange oneor more blocks one beside the other in a space-saving way with orwithout physical separation. Inside each block, the central arrangementof the heat-exchange chamber provides for an inexpensive constructiondue to short lines for the combustion air delivered to the fluidized-bedcombustion chambers, which combustion air is preheated in theheat-exchange chamber or in other suitable means. Each fluidized-bedcombustion chamber may be connected with the associated fluidized-bedcooler to form a static unit, where the fluidized-bed cooler can bedesigned as a mounted construction or can be suspended from thefluidized-bed combustion chamber. A particularly space-saving design ofthe firing system is obtained in that the distance between the firstfluidized-bed combustion chamber and the first outer wall as well as thedistance between the second fluidized-bed combustion chamber and thesecond outer wall of the heat exchanger chamber is 0 to 2 m.

The firing system in accordance with the invention is designed for bigplants. In general, the cross-sectional area of each of the twofluidized-bed combustion chambers, measured in a horizontal plane and athalf height of the interior of the chamber, will be 50 to 300 m² andpreferably at least 70 m². Usually, the interiors of the first andsecond fluidized bed combustion chambers will be approximatelyrectangular in horizontal cross-section. For very big plants, two ormore heat-exchange chambers and at least three fluidized-bed combustionchambers can be arranged side-by-side alternatingly.

BRIEF DESCRIPTION OF THE DRAWING

Further embodiments will be explained with reference to the drawing,wherein:

FIG. 1 is a schematic representation of a first variant of the firingsystem in a longitudinal section along line I—I of FIG. 2,

FIG. 2 is a cross-section along line II—II of FIG. 1,

FIG. 3 is a second variant of the firing system in a representationanalogous to FIG. 1, and

FIG. 4 is a bag plant with two heat-exchange chambers in arepresentation analogous to FIG. 2.

SPECIFIC DESCRIPTION

The plant in accordance with FIGS. 1 and 2 centrally comprises aheat-exchange chamber 1 with a rectangular cross-section of FIG. 2. Thefour vertical outer walls of the heat-exchange chamber 1 are designatedwith the reference numerals 1 a, 1 b, 1 c and 1 d. Adjoining the firstouter wall 1 a a first fluidized-bed combustion chamber 2 is provided.At the opposite wall 1 c a second fluidized-bed combustion chamber 3 isprovided. To the left fluidized-bed combustion chamber 2 two separators5 and 6 are connected, and two separators 7 and 8 correspondingly belongto the right fluidized-bed combustion chamber 3. Each separator has agas-carrying discharge line 9, which opens into the upper portion of theheat-exchanger chamber 1, cf. FIG. 1. Any number of separators maybeused. As separators, there may for instance be used cyclones known perse or baffle plate separators.

The solids separated in the separators 5 to 8 are delivered through line11 to a fluidized-bed cooler 12 or 12 a know per se. Details of thefluidized-bed cooler can be taken for instance from EP-B-0365723 andDE-A-4135582. If desired, solids separated in the separator can directlybe introduced into the nearest fluidized-bed combustion chamber via abypass line 11 a. This is repressented in the drawing for a betterclarity only for the chamber 3 in FIG. 1. If fluidized-bed coolers 12and 12 a are completely omitted, the solids coming from the separatorsare introduced into the fluidized bed combustion chambers via suchbypass lines.

Each fluidized-bed cooler is equipped with at least one line 13 forsupplying fluidizing gas, e.g. air. It also has cooling elements 14 andan outlet 15 for cooled solids. Through the passage 16, part of thecooled solids are introduced into the fluidized-bed combustion chamber 2together with gas. One variant is illustrated together for the heatexchanger 12 a and the fluidized-bed combustion chamber 3 in FIG. 1,where line 16 supplies cooled solids, and line 17 supplies heatedfluidizing gas to the chamber 3. Solid, granular fuels are supplied tothe chambers 2 and 3 through the lines 18, and oxygen-containingfluidizing gas, e.g. air, is supplied via line 19. The fluidizing gasfirst enters a distribution chamber 20 and then flows upwards in thechamber 2 through a grid 21. Further points for supplying gases andsolids can easily be provided.

Suitable fuels include in particular anthracite coal, hard coal,lignite, wood, or oil shale. In addition to solid fuel there may also beused pasty, liquid or gaseous fuels, e.g. refinery residues or variouswastes. The combustion temperatures in the fluidized-bed combustionchambers 2 and 3 lie in the range from 700 to 950°.

A hot gas-solids suspension leaves the fluidized-bed combustion chamber2 or 3 at the upper portion thereof through an opening 23 and flows intothe associated separator, in which the solids are largely separated. Thehot gases leave the separator through line 9 and are cooled in theheat-exchange chamber 1. The chamber 1 is equipped with numerousheat-exchange elements 24 for an indirect cooling of the hot gas, whichelements are represented in the drawing only schematically. The elements24 on the one hand serve to generate steam from boiler feed water, wherehigh-pressure steam with a pressure in the range from 70 to 350 bar andmedium-pressure steam with a pressure of 20 to 80 bar can be generatedat the same time or alternatively. One or more of the elements 24 canalso be used for preheating the air which is then introduced ascombustion air into one of the fluidized bed combustion chambers 2 and3.

The plant is designed for large throughputs, so that the individualparts of the plant have correspondingly large dimensions. Thecross-sectional area of the interior of the heat-exchange chamber 1,measured in a horizontal plane at half height of the chamber 1, lies inthe range from 150 to 500 m². For each of the fluidized-bed combustionchambers 2 or 3 the inner horizontal cross-sectional area, measured athalf height above the grid 21, is 50 to 300 m². The height of a chamber2 and 3, measured above the grid 21, lies in the range from 20 to 60 m.The horizontal width (a) of the common walls 1 a and 1 c, cf. FIG. 2 is10 to 40 m.

To the firing system, there may be connected a power plant with anelectric power capacity of 200 MW or more. To optimally utilize thesensible heat in the firing system, all hot walls may be designed asmembrane tubular walls, through which flows a cooling fluid. Cooled gas,which leaves the heat-exchange chamber 1 through the outlet 25, issupplied to a gas cleaning system not represented here.

As already explained in conjunction with FIGS. 1 and 2, the plant inaccordance with FIG. 3 comprises a central heat-exchange chamber 1, twofluidized-bed combustion chambers 2 and 3, and separators 5 and 7. Thelines 23a connect the fluidized-bed combustion chambers 2 and 3 with theseparators 5 and 7. Identical reference numerals as in FIGS. 1 and 2have the meanings as stated in the description thereof. Thefluidized-bed combustion chambers in accordance with FIG. 3 have adownwardly wedge-shaped design.

In the plant in accordance with FIG. 3, there is a distance of not morethan 2 m between the outer wall 1 a of the heat-exchange chamber 1 andthe fluidized-bed combustion chamber 2, over which distance line 11passes through to the fluidized-bed cooler 12. The same distance alsoexists between the wall 1 c and the fluidized-bed combustion chamber 3.Since the separators 5 and 7 are disposed above the chambers 2 and 3,the block is high and requires little ground area.

In the big plant schematically represented in FIG. 4 in a horizontalsection, two heat-exchange chambers 1 and three fluidized-bed combustionchambers 2, 3 and 4 are put side-by-side alternatingly. The separatorsare provided with the reference numerals 5 to 8. In contrast to the rowarrangement shown in FIG. 4, the chambers may be arranged together withfurther heat-exchange chambers and/or fluidized-bed combustion chambersto form altogether a cross, an L or T in a horizontal section.

What is claimed is:
 1. A solid fuel fluidized-bed steam-generatingfiring system in a block form, comprising: a vertically elongatedheat-exchange chamber of substantially rectangular horizontal crosssection delimited by four outer walls and having an interior height ofat least 10 m; a plurality of heat-exchange elements in said chamber forindirect heat exchange between hot gas in said chamber and cooling fluidin said elements, at least one of said elements being traversed by waterfor conversion to steam; a first vertically elongated fluidized-bedcombustion chamber disposed along one of said outer walls and a secondvertically elongated fluidized-bed combustion chamber disposed alonganother of said outer walls opposite said one of said outer walls forproducing hot gas by combustion of solid fuel therein, saidfluidized-bed combustion chambers having interior heights of 10 m to 60m and means for supplying solid fuel and fluidizing gas to saidfluidized-bed combustion chambers; at least one gas/solids separatorconnected to an upper portion of each of said fluidized-bed combustionchambers for separating solids from hot gas produced in the respectivefluidized-bed combustion chamber, said gas/solids separators extendingalong outer side walls of the respective fluidized bed combustionchambers on opposite sides thereof from said heat-exchange chamber;respective gas-carrying discharge lines connecting upper portions ofsaid gas/solids separators to an upper portion of said heat-exchangechamber for delivery of hot gas thereto, whereby hot gas is cooled insaid heat-exchange chamber in indirect heat exchange with said elementsand a cooled gas is discharged at a lower portion of said heat-exchangechamber; and at least one fluidized-bed cooler for each of saidfluidized-bed combustion chambers, located directly below a respectivegas/solids separator thereof, connected with the respective gas/solidsseparator by a solids-carrying line to cool solids received from therespective gas/solids separator, and connected with the respectivefluidized-bed combustion chamber with a respective line carrying solidsor gas thereto, a distance between each of said fluidized-bed combustionchambers and the respective outer wall is 0 to 2 m.
 2. The solid fuelfluidized-bed steam-generating firing system in block form defined inclaim 1 wherein said fluidized-bed combustion chambers have half-heightcross sections in horizontal planes of 50 to 300 m².
 3. The solid fuelfluidized-bed steam-generating firing system in block form defined inclaim 1 wherein horizontal cross sections of said fluidized-bedcombustion chambers are approximately rectangular.
 4. The solid fuelfluidized-bed steam-generating firing system in a block form defined inclaim 1, wherein said chambers form a row and have a width transverse tosaid row of 10 to 40 m.
 5. The solid fuel fluidized-bledsteam-generating firing system in a block form defined in claim 1wherein at least two of said heat exchange chambers and at least threeof said fluidized-bed combustion chambers are provided in a row withsaid fluidized-bed combustion chambers alternating with saidheat-exchange chambers along said row.